Controlling system



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Dec- 23 l941- e; o. FAIRCHILD Erm. 2,267,632 i y CNTROLLING" SYSTEM Fnac; Api-i1 17, 1937 2 sheets-sheet 1 Nido ATTORNEYS Dea 23, 1941.

Patented Dec. 23, 1941v i'x; i J

v -UNlTED STATES PATENT OFFICE CONTBOILING SYSTEM Charles 0. Fairchild, St. Albans, and 'Vozcan I.. Parsegan, New York, N. Y., assignors to Charles J. Tagliabue Mfg. Co., New York, N. Y., a corporation of New York Application April 17, 1937, Serial No. 137,588

21 Claims.

This invention relates to controlling systems, particularly of the type described in the Fairchild Patent 1,970,559, granted August 21, 1934, which type includes a light source, a phototube (or other photoelectric receiver), a mirror galvanometer, and associated controlling circuits. It also relates to improved instruments of the class including recording and controlling and, as in page 1, column 1, lines 20-28 of said patent, a recording or.

tion of the electrical control system according to the aforementioned application characterized by the use of a capacitor and an associated resistor or resistors permanently connected in the relay circuit pertaining to the governing circuit to secure different rates of response in the governing circuit for determining the rate of restoration of the current therein, without the intervention of any relay-controlled contacts.

As in the system described in the aforemen-4 tioned application, the beam of light from the galvanometer mirror in the system of the present invention is focused upon the plane of a controlling edge of the photoresponsive receiver and moves in correspondence with variations of a controlled quantity, swinging to and fro across the edge, and, through its effect on the receiver,

operates relays which control a reversing motor,

this motor being used for driving any suitable final control element for actuating a measuring or controlling device. As before, the phototube is not a calibrated element but serves only to detect displacement of the light vbeam with reference to the controlling edge and, in cooperation with the rest oi the circuit, to drive the reversible motor in one direction or the other during a displacement, and to hold the motor against rotation when the light beam is in a normal position corresponding to no deflection from its socalled zero position.

It will be evident from the following description that the performance of the instrument of the aforementioned application is improved upon. As before, included in the ampliiier circuit are two relays, one of which is adjusted to close at a different value of current from that required by the other, these two relays having electric contacts connected to a reversing motor which contacts are so arranged that when one relay is closed and the other open the motor stands still, and when both relays are closed or both open the motor runs respectively one way or the other, both relays being open when the light beam does 5.. not shine upon the receiver and both closed 'when all of the beam, or a sufficient part of it, does shine on the receiver, and one relay will be closed and the other open when a smaller fraction of the beam falls on the receiver, the beam l .in this case being split by the controlling edge.

` 'These relays carry additional contacts, generally as before, for the application of an advancing E. M. F.to the galvanometer, the utility of which is also explained in 'the Fairchild application 3 mentioned above.

'This invention diiers from that described in the abovementioned application by (1) the elimination of relay-operating contacts from the ampliiler grid circuit, (2) the arrangement of this V`@circuit to provide a varying time-constant, (3)

the use of higher opening than closing relay currents which causes the balancing to be nished by a series of extremely short steps and makes .possible such steps in detecting small departures zg@n from a balance, independently of the galvanometer period, and (4) the addition of resistors of appropriate magnitudes so cooperating with relay contacts that the relay operation does not undesirably affect the plate current. 'Ihe selection of the particular magnitudes of the resistors of (2) and their cooperating capacitor needed to provide the variable time-constant of item 2 is an important feature of the invention and since they have a critical bearing upon the operability A of the systemdescribed, are adequately disclosed herein.`

' Thus, the chief object of our invention is to provide improved methods of and means for causing a sensitive galvanometer to accurately i" and most rapidly return a deiinite balancing point.

These and such other objects of our invention will appear to those skilled in the art from the accompanying drawings and specification, in

which are illustrated and described a specic embodiment of our invention. It is our intention to claim all that we have disclosed which is new and useful.

lIn the iigures, like characters of reference indicate like parts throughout and are generally as in the aforementioned Fairchild application, diierences in sense being shown by the use herein of the double-prime: Fig. 1 is a diagram of our electrical measuring circuit together with the improved phototube circuit with the amplifier,

relays and lamp, with which it cooperates; and Fig. -2 graphically illustrates the variation of plate current with phototube illumination; both being plotted against time as the illumination is suddenly increased.

In the normal condition of balance, the potential of the thermocouple 21, whose temperature is to be measured, corresponds with that of the point 42 of contact of the sliding contact 4I and its slidewire I8 and there is consequently then no current owing through galvanometer 38 which is connected with both thermocouple 2-1 and the sliding contact 4I through contacts 35 and 36 which are kept closed during ordinary operation and only opened manually during standardizing of the potentiometric circuit when contact 36 is closed with contact 31. In its balanced (zero-current) condition, the galvanometer directs its reflected light beam so that the beam is half on the phototube as shown in Fig. 1.

A departure from the latest steady temperature causes the galvanometer to move to alter the illumination of the phototube 6I in the opposite direction from the change of temperature, i. e., upon a fall of temperature the galvanometer swings the beam in a counterclockwise direction onto the phototube and vice versa.

A change in the illumination of the phototube 6I affects the photoelectric current in the same direction which similarly affects the potential of the governing grid 61, i. e., an increase of illumination and of the photoelectrc current act through the if change in resistor 13 to correspondingly raise the grid potential.

Two time-constants for the gn'd potential are provided to cause it to change rapidly with a iirst small iixed time-constant immediately after a sudden change of illumination and then very slowly relatively with a second much larger xed time-constant. This double time-constant is produced by capacitor 88 and its shunting and series resistors 13 and 89 respectively.

I n this arrangement, a sudden increase, e. g., of the photoelectric current in effect shorts out capacitor 88 initially so that the ir change due to the photoelectric current in its divided path through resistors 13 and 89 would cause an lnstantaneous rise in the grid potential if it were not for the small distributed capacity, e. g., auf. of the circuit connecting the amplier grid 61 and the phototube cathode 65 with one end of resistor 13 and with one side of capacitor 88. The effect of this small distributed capacity is to cause this circuit to have a deiinite though very small tirne-constant so that the initial potential change is 90% complete in less than 174mm second and the plate 64) current. in the coils 89 and 1D of the relays responds very rapidly also in spite of the appreciable impedance of these coils. The second time-constant is due to the storage of current in capacitor 88 which builds up a potential across the capacitor that causes an increasing current to flow through resistor 13 due to its ir drop until resistor 13 carries substantially all of the photoelectric current and capacitor 88 carries substantially none of it. at which time the capacitor ls normallycharged and conditions are steady. For the purpose of the above explanation in this paragraph, it has been assumed that the galvanometer has irst been, held steady for awhile in its normal position for directing the beam as shown in Fig. 1 but with the light 19 out` and that suddenly the light was turned fully on. In other words, the actions of the relays, motor II2 and galvanometer have been disregarded in the foregoing description to better bring out the characteristics of the circuit itself.

It is seen that the permanently connected capacitor in the highly sensitive governing cir- 'Cross Reierence cuit produces a double time-constant therein but without requiring the additional relay-operated contacts used in momentarily connecting an additional capacitor into the governing circuit, a change which is seen to be a considerable improvement in that it permits the initial response tp be nearly complete in j/iooo second instead of having t o wait for the relays to act which takes of the order of ten times as long. This change makes possible a much faster balancing action than was possible with the device of S. N. 131,843.

Instead of relying for a stepping action upon the response of the galvanometer to the removal of a large advancing E. M. F., this function is better handled by providing the relays I I and I2 respectively with resistors IOI and IDO which cause them to oscillate by making their opening current values higher than their closing current Values (referring to the plate current). Capacitors |01 and |08 cooperate in timing the relay oscillations.

The relays I I and I2 are provided with backcontacts which close when the relays are open, i. e., with their armatures most distant from their coils (both armatures being continuously mechanically biased toward their open positions), to then insert resistors IDI and |04' respectively in the plate circuit to thus keep the impedance of the plate circuit substantially constant for all eXtreme positions of both relays.

TBE PoTsN'rroMmrc Cmctnr Fig. 1 shows a potentiometer circuit generally similar to that shown in the aforementioned Fairchild application, and in which current from a battery I3 flows through a conductor I4, a manually-adjustable rheostat I5, conductor I6, to a divided or bridge circuit having in one arm resistor I1, slide-.Wire I8 shunted by resistor I9, and resistor 2D, and in the other arm resistors 2| and 24. when the circuit is balanced, then to resistor 25, conductor 28 and back to battery I3. Conductor 30 is permanently connected through conductor 29 to connection 28, with which only two pairs of relay contacts respectively 41, 48 and 49, 50 are connected. The potential of 28 is lowered by shunting resistor 24 with resistor 51 through conductors 59, 55 and 29 and contacts 48 and 4,1 when both relays II and I2 are open, or is raised by shunting resistor 2| with resistor 5 8 through conductors 60, 29, 55, 56 and contacts 50 and 49 when both relays are closed. By properly choosing the values of resistors 5l and 58 the potential of 28 can be changed by any amount required. Provided the resistance of slide-wire I8 and its shunt I9 are not too large in comparison with the resistances of galvanorneter 38, thermocouple 21 and resistor 3l, the eiect of this potential change on the deflection of the galvanometer will be suiiiciently constant while 4I moves across the slide-wire, being least when 4I is in the middle and greatest when 4I is at either end. It is not essential to have an exactly constant eiect. It will be shown in the description following the operation of relays II and I2 is such that resistors 24 and 2l are not both shunted at the same time by resistors 51 and 58, but only one at a time. It will be apparent that the arrangement is such that the potential of point 28 takes only three xed values, the intermediate one corresponding with a balanced condition of the potentiometer with relay I I closed and I2 open and two others, when both relays are closed or both open. The slidewire I8 is calibrated with reference to the center normal value of the potential of the point 28.

Examine' The current 'through the slide-wire is standardized by manually throwing switch 34 to .the reverse direction from that shown, to connect the standard cell 43 opposed to the battery, by the connection 44 through resistor 45, contacts 31 and 38 of switch 34, galvanometer 88, resistor 3|, conductor 39, bar 40, contacts 4| to the point 42 on slide-wire I8, when 42 is at a predetermined position selected for convenience. While the above description is adequate for the present purpose, this is also explained in the Fairchild Patent No. 2,207,344, granted July 9, 1940.

Tmc GovimNrNc Cmcurr In Fig. 1, the balancing power-circuit or governing circuit is shown to be electrically independent of the potentiometer-circuit, and to include the phototube 6I, connected with its anode 62 through conductor 63 to plate 84, and its cathode 85 through conductor 88 to grid 81, of triode 88. Transformer 1| is used to supply the various voltages of this circuit, no auxiliary rectiers being used for the two tubes. Grid 81 of tube 88 is connected through conductors 68 and 12, resistor 13, conductor 15 to what is commonly called the negative terminal of the secondary of the transformer 1I. Filament 16 of tube 68 is connected through conductors 11 and 18 to a low voltage section of the secondary. Lamp 19 is also connected to a low voltage section in the secondary through conductors 14", 11 and 80. Plate 64 is connected to the so-called positive terminal of the secondary through conductor 83. Synchronous motor 84 may be connected if required, as for driving a record chart, to the transformer through conductors 85, 88 and 80. Grid 81 is also connected through conductors 86, 12, 81, capacitor 88, resistor 89 and conductor 96 (capacitor 88, resistor 89 and conductor 96" being shunted by resistors 18 and 91), and thence through resistor 98, and conductors (hereinafter leads) 90" and 18 to iilament 16.

Capacitor 88 with its net-Work of resistors 13, 89, 91 and 98 is permanently connected in the governing system to provide said system with a double time-constant as regards the response of the grid potential to a change of the illumination of the phototube. For purposes of the present analysis, it may be considered that the circuit which includes the phototube cathode 65 and the amplifying-tube grid 81 has a distributed capacity of puf. between line 12 and line 15. Adopting the convention of the polarity illustrated on Fig. 1, line is at the lowest potential and line 83 and anode 62 of the phototube are at the highest positive potential.

Suppose the mirror galvanometer be held steady so that the light beam would split shielding edge 54" for the phototube if the light 19 were turned on, but it is assumed that light 19 has been turned off for a long enough time sc that the conditions of the governing system and of the relays and driving motor H2 are also steady. In other words, both relays are open and slider 4l is moving upscale (to the right in Fig. l) at the full speed of the motor.

Now suppose that the light 19 is suddenly turned fully on to give half-beam illumination of the phototube. Instantly the photoelectric current of a few mlcro-amperes ows through wires 66 and 12 so that there is a suddenlyapplied flow of current through a split circuit which consists essentially of capacitor 88 and resistor 13 in parallel.` 'During the sudden change of the current, the impedance of capacitor 88 is momentarily negligible. Consequently at this instant, the relative ows through resistor 13 and capacitor 88 depend primarily on the relative values 'of resistance of 13 and that of 89 which is in series with capacitor 88, the resistance of 89 being relatively so low that most of the current then flows through it. Thus, when the light rst strikes the phototube and starts an instantaneous now of photoelectric current which proceeds as though capacitor 88 were shorted, there is an instantaneous ir change across the resistance 89 which would cause the grid potential to be instantaneously raised but for the small associated distributed capacity of, e. g., 5 paf. aforementioned which causes the circuit to then have a definitely iixed initial time-constant of a far different order (i. e., one giving a much higher rate of response) than that due to capacitor 88 and its associated resistors after this initial eil'ect has been exhausted. As later described more fully, the initial very rapid change of the grid potential causes a corresponding change of the relay current to cause relay Il to close and thus stop the motor and slider.

As soon as the initial jump of the grid voltage is over, a much more gradual further change occurs in the same direction and the net timeconstant for the circuit (from then on as long as the illumination remains constant) may be considered to be due to the building up of a potential in consequence of the storage of the photoelectric current in the capacitor 88 and the accompanying driving of the photoelectric current through resistor 13 as the potential across capacitor 88 builds up.

It takes less than lAnco second for 90% of the initial sudden change to occur with the initial time-constant due to the effect of the distributed capacity of 5 puf., while it takes more than 4 seconds for 90% of the remaining change to occur with the time-constant due to the eiiect of 0.02 nf. capacity of 88. Where the time-constants are of such diierent orders, it is clear that they may be considered separately and additively. In other words, in eiect, the circuit has unquestionably a small xed time-constant initially giving a very rapid rate of change fol- `lowed by a much larger effective time-constant which produces a much lower rate of change of the grid potential in response to changes of the illumination of the phototube. In spite of the appreciable impedance of the relay coils, the

'initial response of the current in the relay coils to a change of the illumination of the phototube is at a very rapid rate and well within a half-cycle oi' the usual A. C. supply, such response-time being, of course, considerably less 'it-han the operating time of the relays.

The various values used in the design of the complete governing circuit are so selected that, upon a sudden swing of the light beam fully onto the phototube from a position in which it :is funy oir the phototube, the effect on the grid (instead of being held iixed as above stated), the

further response. of the sadcunrent value due to. saidl overswing is so. retarded that both the galvanometer and the motor have time to come to rest before the relay I2 could possibly operate, due to such overswing. Cooperating with this slower response are: the removal, by the closing of relay Il, of the advancing E; M. F. which caused the galvanometer to lead the sliding contact enough to provide time for both to come to rest, and the self-generating oscillations of relay II which cause the forward movements of the sliding contact to be small on the near side of the dead-zone surrounding the balancing position.

Relays Il and |2 are connected in the plate circuit between the transformer lead 9|" and filament 16. The path of the current, when the two relays are open, is from transformer lead 9|", lead 93", relay coil 10 shunted by resistor |00, lead 32, contacts 95 and |06, lead 5I, lead 82, relay coil 69, lead 23", contacts 94", |03, lead 22, leads 8|, 18 to filament 16. When the relays are both closed, the current ows from leads 9|, 93", and divides; part of it proceeds through coil 10 and its shunt resistor |00 to resistor |04', to lead 82; and the other part proceeds through resistor |04, contacts |05, lead and also to lead 82. The whole current continues through lead 82 and is again divided between two paths; one part through relay coil G9. resistor IOI to lead 8|; and the other part through resistor |0|, contacts |02, |03, lead 22" also to lead 8|; the whole current then continues through leads 8|, 18 to filament 16. It is evident that. in the open position, resistors |04' and |0| are shorted by contacts |06, 95" and |03, 94" respectively. Fig. 1 shows the relays in the balanced position, i. e., with relay closed and relay I2 open.

Resistor IOI' is in series with coil 69 of relay II. However, in the open-relay position, resistor IOI is shorted, rendering it ineffective, through lead 23", contacts 94", |03 and lead 22". When relay I| closes, contacts 94", |03 break, thus unshorting resistor |0I, and decreasing the plate current; and the relay current is further reduced by the insertion of resistor I0| as a shunt to relay coil 69 and series resistor |0I, through contact-s |02, |03 and lead 22".

Similarly coil of relay I2 is in series with resistor |04'; but in the open-relay position, resistor |04' is shorted through leads 32, contacts 96", |06, and lead 5|". When relay I2 closes; contacts 95", |08 break, the current flows through coil 10 and resistor |04; and resistor |04 shunts coil 10 and resistor |04 (which are in series) through contacts |05, |06, and lead 5|. Resistor |00, when used, reduces the current through coil T0 at all times, i. e., regardless of whether relay I2 is open or closed Resistors I0| and |0I' are so chosen that when the relay closes, the current through coil 69 is sufliciently reduced to. allow the relay to open at any desired value of total. plate current, but the net electrical impedance between leads 82 and 8| is maintained nearly the same. This prevents any significant change of plate current because of the relay operation. Resistors |04 and |94 are likewise so chosen that when the relay I2 closes, the current through coil 10 is reduced and relay l2 may open again at any desired value of. total plate current. Similarly the net impedaaioe between leads 82,- 93" is maintained nearly constant so that no significant change of Cross Reference total plate current. occurs when this relay operatei.

Inorderto prevent the relays from chattering because of the half-wave rectication of triode E8. relay II with its resistors is shunt-ed by capacitor |01, and relay I2 with its resistors is shunted by-capacitor |08, and the two are shunted by capacitor |09 connected to conductors 8| and 93". These three capacitors serve to smooth out the intermittent direct current and the variable magnetic flux in the relays, and to absorb quick surges of plate current, thus tending to greatly increase the stability of relay operation. In the succeeding paragraphs referring to the functioning of the transformer secondary circuit,

all voltage references pertain to the R. M. S. voltages at the instant when the plate lead 83 ls most positiverelative to grid lead 15.

The potential of plate 84 relative to filament. 18 varies from about 160 volts to about 80 volts as the plate current increases.

Grid 61 potential is maintained negative, relative to filament 16, by means of the transformer secondary 14" and by the potential drop across Y relays |I and I2 which are in series with transformer secondary 14". The negative voltage source is from lament 16 through leads 18, 8|, relays and I2, leads 93", 99, transformer secondary 14, to lead 15. The voltage of transformer secondary 14" is constant, but the potential drop through the relays increases with increasing plate current.

Resistors 91, 98 shunt the negative potential source from lament 16, leads 1 8. 9 resistors 98, 91 to lead4 1,5. and a desired negative voltage may be chosen by proper ratios of resistors 91, 98. Proper negative potential at gridl1Y is maintained by a proper choice. of resistor 13 and also of capacitor 88 and resistors 89, 9B. At any instant the potential drop from larnent 15 to grid 61 plus the potential drop across resistor 13 equals the potential drop from filament 13, through relays I, I2 and transformer secondary 14 to lead 15. Also at the same instant, the potential drop from lament 16 to grid 61 plus the potential drop across capacitor 88 resistor 89 lead 96" equals the potential drop across resistor 98. The order of the magnitudes of the various resistors, including 91 and 89 and of their cooperating capacitors including 88 provides satisfactory operation in most industrial applications.

Resistor 91 25,000 ohms i 50% Resistor 98 5,000 ohms 1- 50% Resistor 89 2 megohms i 50% Resistor 13 75 megohmsi 50% Resistor IOI 7,000 ohms i 20% Resistor |0I. 10,000v ohms i 20% Resistor |04 6,000 ohms 1- 20% Resistor |04' 9,000 ohms r 20% Resistor |00 12,000 ohms :l: 20% Capacitor |01 3mfd.

|08 lmfrl +2009 @rasero 88 0.02 mfd. +300% or-50% Relay coils 69 and 10, impedance at 60 cycles 50,000 ohms+or-20%, resistance 5,000 ohms-|- or-20%. Transformer. voltages for 60 cycles Leads 15-99 100 volts n 91"-83 20o voits} i m/U The phototube 8|, when'v dark, has very large resistance' and in effect ants as an open circuit. When,illi1ininated. its effective resistance de- LXBmIHET creases proportionately with the illumination and 100 megohms is the order of its magnitude with the light fully on the phototube as used in this instrument. Its anode 62, connected through lead 63 to plate 64, is maintained positive relative to its cathode 65 connected through lead 86 to grid 81. The phototube may then provide a path for electron ow between grid 61, lead 66, phototube 6I, lead 83 to plate 84, thus in eifect applying a positive potential to the grid varying with illumination and superposed upon the negative bias supplied by the secondary 14". The phototube current through lead 86 is supplied by electron flow through resistor 13, through resistors $1 and 89, capacitor 88 and leads 8l, 12. The:

negative potential of grid 61 relative to filament 'i6 can vary only as fast as the potential variation of leads 12 relative to lament 18. Similarly,

the grid bias varies directly with a change in potential across resistor 98, lead 96", resistor 89, capacitor 88 to leads 81 and 12. The tube capacitances of triode 88 are relatively small and therefore cause very little delay in change of grid potential with change of illumination. But capacitor 88 is of relatively larger capacity and hence may delay grid potential changes considerably.

At the instant the phototube 8l is illuminated there occurs a surge of current (see Fig. 2) through resistor 89 and capacitor 88. The immediate change of potential drop across resistor 89 causes a quick change of plate and relay current. The potential across capacitor 88, however, varies more slowly as it is charged or discharged, attaining-its ultimate value much more slowly. The potential of grid 61 relative to filament 16, first receives a quick change and then a more gradual one, this latter condition continuing until capacitor 88 has attained its final charge for the particular value of illumination of the phototube. This quick and slower change in grid potential causes a corresponding quick and slower change of plate current through the relays. The amount of quick change and the rate o slow change of the plate current are controlled by the values given to resistor 89 and capacitor 88. Resistor 13 allows the capacitor to discharge, whenever the illumination of the phototube BI decreases, at a rate depending upon the value of this resistor and capacitor 88.

The nature of this quick and slower change is illustrated in detail by Fig. 2. One curve shows the increase of illumination as the beam is suddenly moved onto the phototube. With only very slight delay, the plate current jumps to a higher value than when the phototube was dark, after which it increases suiiiciently slowly to allow the galvanometer to attain its balance in a manner soon to be described. Normally the light beam, in returning to the balance point, will swing beyond the controlling edge because of the time delay in the increase of plate current and the closing of relay I I, and because of galvanometer momentum. It is necessary that relay II shall close as quickly as possible, but that the plate current shall be suiciently delayed behind the illumination value to prevent relay I2 from closing too quickly while the galvanometer iinds its dead zone of stable balance.

Fig. 2 illustrates that the plate current at no illumination remains, e. g., at approximately 3 m. a. When the phototube is quickly illuminated by the beam, this current immediately jumps to approximately 8 m. a., which is suiiicient to close, and maintain closed,- relay II. ,This current value corresponds to the sudden increase of voltage drop across resistor 89. 'iherearter, the plate current increases more slowly, corresponding to the slower potential change of capacltor 88, so that although the instantaneous value of phototube illumination corresponds to a current value considerably higher than the closing of relay l2, the plate current increases so slowly that the closing current of relay I2 is not reached before the light beam has returned to within the dead zone. This gure shows that our circuit, without contacts and switches in the grid circuit, has successive rates of change of the plate current with a sudden change of illumination) oi the distinctly dinerent magnitudes required.

It is found that the use of relays II and I2, connected in series with transformer secondary 14 as shown in Fig. l to supply a common path to the plate and grid circuits, results in increased ratio of plate current change to change in phototube illumination, that is, the circuit is more sensitive to deflections of the galvanometer.

THE Moron Cmccrr The main purpose of the relays is to operate motor I l2, indicated as a shaded-pole motor having a main coil connected to the line and having two shading coils H3 and II4 for reversing the motor. Contact IIS on relay II and contact H8 on relay I2 are connected through conductor I I1 to both coils H3 and IH of the motor. Contact II8 on relayl II is connected through conductor IIB to coil H3, 'and contact |20 on relay I2 is connected through conductor I2I to coil I I4. The arrangement is such that motor II2 is braked to a standstill when relay II is closed but runs contact 4I downscale when both relays are closed and in the other direction when both relays are open.

DESCRIPTION or OrEnA'rroN The following rsum of the principal parts of the electrical circuits and their functions is included here for ready reference in reading the detailed description of operation and appended claims; first taking up, under A-D, that which has been earlier disclosed in the aforementioned patent and applications and then, under E-G, describing that which we believe to be new in this general combination:

A. Potentiometer circuit B. Means for advancing the phase of the galnanometer In the balanced condition of the potentiometer, i. e., with the galvanometer at its normal position with no current flowing through it, relay I I is closed and relay I2 open, the light-beam being split by the controlling edge. In this position of `the relays, point 28 is at its normal potential. When the relays are both open, or

both closed, the potential of point 28 is lowered 'or raised respectively, changing this potential i'neach case so 'that the galvanometer deiiection is less than it would be without cooperation with the relays. These changes in the potential of point 28 result in an advance of the position of the galvanometer with reference to that of the moving contacts 4I, as both move towards the balance point.

C. Reversible motor circuit Ashaded-pole reversible motor has its shading coils H3, H4 respectively connected to the contacts H5, H8 and H6, IZD of relays II and I2. In the balanced condition, both coils are shortcircuited yby said contacts and the motor is stationary. When both relays are open, only coil H4 is shorted thus driving contacts 4I upscale;

and when both relays are closed, only coil II3 is shorted thus driving contacts 4I downscale.

D. Photoelectric and amplier circuit This includes the phototube 6I, amplifier tube 68, light source 19, transformer 'II and relays II and I2. nected with the potentiometer 'or reversible motor lcircuits but cooperates with these through relay contacts. An increase in the phototube illumination tends to increase the current in the relays to cause them to close.

E. Grid circuit of amplifier The grid circuit of the amplier includes, in

special arrangement, capacitor 88 and resistor;

A8S, the two in series being shunted by resistors 'I3 and 97. The grid return connection traverses the relay circuit through conductors 99, 93 and 8| to the filament. This circuit is so designed that sudden illumination of the photocell resuits in a sudden change of grid voltage and hence of plate current to a predetermined value within the dead zone of balancing, followed by 'a slow rise. It may be parenthetically noted kthat the inclusion of the relays in the grid return circuit increases the amplication of `the photoelectric current.

F. Relay opening currents greater than closing currents This means that if a current between the opening and closing values ows through the relay coils, the relays will oscillate. This is ac- 'complished by shunting coil 69 of relay I I with resistor IDI and coil 'I0 of relay I2 with resistor 104, these resistors being connected across series resistors as described. The periods of oscilla- 4tion are controlled by shunting capacitors 101 'and I 08, being chosen in any particular case in lrelation to the impedances of the relay coils and series and shunting resistors according to the requirements such as scale range, galvanometer sensitivity and reversible motor speed.

The condition of the relays H and I2 for various plate current values is shown diagrammatically in Fig. 2. It will be seen that, for example, a current of 5 m. a. is suiicient to close relay II but, as soon as the relay is closed, the shunt resistor I I cuts the current through the relay down to such an extent that the relay opens again. This closing and opening of the relay (oscillation) will occur in the illustrated embodiment as long as the plate currentI is within a range from -8 m. a. but above 8 m. a. the 'relay will remain closed as the shunt resistance is se- The circuit is not electrically con-l UTOSS HGTGFBHCG lected so that it 'do'es not cut ydown this (or a -higher) value oi current ihr enough to cause opening of the relay. The Esame action occurs with the relay I2 except that its opening and closing currents and oscillation range are al1 at higher values as indicated.

G. -Stabili-zing plate circuit during relay operation Additional resistors IOI' and IIJL'I on relays I .I and I2 cooperate with back contacts 94" and to maintain the impedance of the plate circuit constant during relayA operation. It may rb e noted here that mirror 38' of galvanometer 38 is provided with ,stop 38" which keeps the image from passing oi of 'phototube 6I when the beam is swung in a counterclockwise direction.

Approaching balance point, light l017 l'uhototabe, both'relays open Having -identied and described the essen -dials of lthe-circuit,iet'us suppose that the E. M. F. dof thennocouple 21 is l`considerably more than `the idierence -in potential between points 28 and 42 in the potentiometer, that the galvanometer 38 is deflected proportionately to this fdifference in potential, and that the beam of light is oi phototube irI on `the far s'ide of ythe controlling edge 54of shield 122,'up in Fig. l. With 'no -light on -photot'ube 6I, grid 6l assumes a sufficiently-high negative bias, and the 'relays are 'both open. Contacts IIl', IIB, connected to the shading coil HG are open, allowing the still- Jsnorted-elfiading coil H4 'to'cause the motor H2 f iniiunce of therestoring torque 'of its suspen- A'sions 'and lof the decreasing potential -diierence between point 28 and the moving point 42. At anyinstantdm'ing this return movement, the galvanometer, because of the retarding effect of its 'back F., would ordinarily lag be- Lhind the positicncorrespondingto 'that of point 12. -Insteaelythe advancing E. M. F. imposed by the change in "potential of point v28 puts the lgalvano'inirter eitherfexa'ctlyin phase with point 'l2 for ahead of it. The ,galvanometer should ideally lead the 'contact suiciently that despite the time involved in lrelay operation, the over- 'run of the `motor -and Athe `accoinpanying move- 'mentor' point 42, both the galvanometer and point l2 'nd 'exact-balance on the one stopping 0f the-motor.

As the lig'ht beam rapidly approaches the controlling edge 54",-illuminat-ion of Athe phototube begins at a vandthe plate current increases as shown jin Fig 2. The vrapid]y-increasing phototube-cur'rent -eauses an initial quick increasejof plate current from its minimum value to s. value sufficiently high to 'close relay AI I and stop the motor.

the'linstant 'when lthe relay current just begins 'the closing dfTeiay n rpomt b in rig. 2), the lilluniination'has 4already passed 'the intensityrforexact balance ('Figq2) and is still rapidly motor 112 Aisjzrayeling at full speed, contact 4I is slightly behind the point of [Himmel .final balance, and the galvanometer is traveling vat full speed beyond the balance point under the inuence of the temporary advancing E. M. F. and of the moving point 42. At the instant after the closing of relay Il, contacts 5 IIS, ||8 close and the motor ||2 and contacts 4| begin to stop; contacts l1, I8 open to break the circuit of resistor 51 and restore point 28 to its original potential, and the galvanometer will of its back E. M. F. and the restoring torque of its suspensions, both opposing its momentum. At the instant when the motor ||2 stops, contacts 4| will be at least approximately at the lthen quickly stop under the combined influencegm point 42 required for exact balance with thegl thermocouple E. M. F. plus the normal potential of point 28, but the galvanometer, although stopping or fully stopped, is well past the point of exact balance and the illumination of the phototube is at the moment considerably highero exact balance under the restoring torque of its 2 5 suspensions, again opposed by its back E. M. F.

Fig. 2 shows that the illumination increases rapidly from point a when the light beam reaches the photocell at edge 54". There is a correspondingly rapid increase of plate current up to and beyond the closing current value of relay so that relay does not oscillate under these conditions. 'I'he illumination continues to increase rapidly as relay II is closing, but the plate current can increase only slowly because of the slower charging of condenser 88, as stated before. Soon after relay is closed, the stopping galvanometer quickly decreases the rate of increase of illumination; this illumination reaching its maximum well above the correspending closing current for relay l2 and slowly decreasing as the galvanometer returns to its exact balance. In this manner, before the plate current can reach the closing current value for relay |2, the illumination will have decreased to a point well within the dead zone, and both galvanometer and contact 4| will stably balance within a very narrow dead zone.

It will be seen that at initial illumination, the plate current quickly rises to a value at c just above the opening current of relay so that, even though the opening current of relay is considerably higher than its closing current, the relay will not be able immediately to open again once it has closed. In other words, the time,`

represented by the distance b to c, on Fig. 2 is smaller than the predetermined time of closing and opening again of relay |l.

In practice, it is in many cases found practicable to advance the galvanometer to such an extent that it is considerably ahead of contacts 4I as they both move towards the balance point. Then when the beam reaches the controlling edge, the relay will close and stop both motor and galvanometer as before. But the contacts 4| will notl have reached the point of exact balance so that, when the galvanometer begins to return from its rst-stopped position beyond the dead zone, it is brought back to the low-current .side of the dead zone, and relay opens but quickly closes again, causing the motor and contacts 4| to take a short step forwards, this being repeated as necessary until exact balance has Vbeen reached. Y

Approaching balance point, lighi fully on phototube, both relays closed When the thermooouple E. M. F. is lowered, the Alight beam is deiiected onto the phototube from `the latest steady value at which the instrument was balanced with relays |I and |2 respectively closed and open and both the galvanometer and the motor stationary, relay I2 also closes (so `that both relays are then closed) thus opening contacts H6, |20 for the shading coil ||4 and allowing the motor to move contacts 4| downscale towards a. new balance, and closing contacts 45, 50 so that resistor 58 shunts resistor 2| and raises the potential of point 28 thus decreasing the galvanometer deiiection. The curves of Fig. 2 may be inverted about the center line of the dead zone, to substantially illustrate the decrease of plate current which occurs when the light beam approaches the balance point from a deflection fully on the phototube. When the beam reaches the dead zone, the plate current experiences a iirst quick and then a slower decrease, quickly opening relay l2 but delaying the opening of relay I| until the galvanometer has found exact balance.

Leaving balance point, momentary opening of relay 11 Assume now that the galvanometer and relays are at exact balance and that the thermocouple E. M. F. is increasing very slowly. The galvanometer experiences a small deiiection off the photocell, and the illumination and plate cur- 'rent decrease slowly until the opening current of relay I| has been reached. Relay then opens, but since the plate current is at that instant higher than its closing current it immediately closes again. This opening and very quick closing make possible a very short step of the motor H2 and contacts 4| upscale. Also during this YVshort step, because of the momentary change of potential of point 28 in the previously described manner, the galvanometer receives a quick impulse in a direction back towards its normal position. This makes possible very short steps, each discrete and positive, with a high enough frequency to follow as rapid a change of thermocouple E. M. F. as occurs in practice.

Leaving balance point, momentary closing of relay 12 A similar action occurs when the thermocouple E. M. F. slowly decreases. The illumination and plate current slowly increase until the closing current of relay |2 has been reached. The relay then closes, but since its opening current is considerably higher it will open again immediately, allowing only a very short step of contacts 4| downscale. Again with each step, the galvanometer is given an impulse back so that undesirable relay hunting oscillation is avoided.

The application of the method of control which is disclosed here is not limited to the use of a reecting galvanometer, source of light and -photoresponsive receiver, nor to the use of two electromagnetic relays operating at diierent currents dening a zone of insensitivity. In a broad sense, we have shown here a system of control in which the dead zone is more of the nature of a trap than of a zone or span limited by xed barriers or real bars. In a mechanical sense, the dead zone does not have stationary limits because, when the measuring element enters it, the near-'side has a tendency to oscilat a predetermined rate; `sind the far side in a sense stretches while the said element lpasses beyond the normal position and returns to it, the controlled means (contacts il) having been stopped (perhaps momentarily) -by the passage of said element through the near side. -It is presupposed 'that the action is dependent-for its success on advancing -the phase of said element with reference to said controlled means, Vfor otherwise the latter would pass `its balancing -position and a reverse action would have to come into play, in which case nothing would be accomplished by permitting the far side of the dead zone to stretchflthat is, Anot act immediately. It is readily apparent that said means must not be permitted to pass the balancing position else the measuring element will not return until the far side of the dead zone -has acted to reverse the control. A

-A similar action could be accomplished with any means which is forced into `electrical--con tact or mechanicalengagement at the near side of a dead zone, while 'the far side is not permitted to act as soon Vas the element lreaches it but is inactive or even removed until the ele- -ment has had time to return tothe normal position. Again, it is supposed that the governed means lags behind the measuring element. Alternatively, also, the abovementioned electric contacts or lmechanical engagements can be used to operate any known type of relays. The system, or method, disclosed -is essentially a relay system in which the governed means travelscon- Cross Reference to in the hereinafter appended'claims, such term 1de'ines consecutively different magnitudes of a damping ieiect. The time-constant refers to an effect regardless vof 'how 'it 'is produced, instead of to a pause. In other words, it is the i time-constant -of a Jresponse `of a 4condition such jas, by way of example, 'a relay current to a Li'i'ange of illumination of a rphototube, instead 'of being iimited toa product -or ratio of values of resistance, inductance and capacitance. The

13 term l`time-constant of response vhas its usual meaning: Aa rate of change of the response per -ur'iit of the -yet-unfullled portion of the repdnse or, alternatively, the time it would take 'the response to be complete if continued at the -rate loi change of the Aresponse at the instant considered. -Mathernatioally expressed, for the response of -curr'ent i`to asudden change of illu- -ini/nation to have-a single time-constant K, the Ycurrent fi -mu'st -have 'the -iollowing exponential z5 relation Awith time "t:

where Eo-is the `ultimate current -ch'an'ge and `e is Athe aNa'pe'rian base. While conventional in- -s'tru'me'nts may be considered to have a plurality of 'time-constants-oi response, these are not limited to damping 'but'simultaneouslm instead of consecutively, -include `either at least a second time-constant or a harmonic function, due to the t-inuously towards the balancing position 'iso long 35 -inertia of the jinstrument, 'having `a generally as the measuring element is deected from its normal position, the speed of travel being o'f an independent and predetermined value.

While there may be some question of the logic of describing the action as a stretching of the far side of the dead zone, rather than as a slowing of response which presents a reaching of the far side; actually however, there is no fundamental diierence, because the measuring element does reach and even pass the normal place or value of the far side of the dead zone. The stretching may be conceived as between illumination and plate current `in a photoelectric method, and a more strict mechanical equivalent would be a exible and temporary seizure of the measuring element within the dead zone While the governed means stops. It is apparent that, in the latter instance, Athere is a definite maximum speed beyond which `it would not be possible to seize the measuring element or member before it passed the dead zone.

The terms and expressions which we have en'i- -pleyed are used as terms of description and not oi limitation, and we have no intention, in the use of such terms and expressions, of excluding -any equivalents of the features shown 'and 'described and portions thereof, but recognize that various modications are possible within the scope of the invention claimed.

Where the word system occurs in the claims, and especially where a governing system is referred to, this is for the means stated to operatively connect vthe sensitive member with a -final controlling element which nal element operates to perform a function related to the value of the member-sensed variable and maybe either an exhibiting means such as an indicator, a pen or other marking device or may be 'a'sliding contact, -a variable controlling-resistor 'or 'any unstabilizing effect.

We claim:

5l. In Ithe-art of -measuring and controlling, the steps inthe method'of stably rebalancing a gov- 40 erning system which is sensitive to an independent physical variable and includes an electrical circuit and a member which is deflectable from a balancing position upon a change in the 'value of the variable, which -steps comprise,

acting Within an operating range `of positions of the member varying the electrical condition in 'the circuit in'responseto deections of the member, continuously but sharply altering the eiective time-constant of response of the condition to 'produce a rapid initial Yresponse directly iollowing a sudden change in the position of the member within said range and a much lower nal `rate of response, and governing the rebalancing of the member to its balancing posi- 'tion in accordance with the value of the damped ma from a galvanometer relative `to a phototube to `produce a'curient ultimately corresponding with such position over a range of phototube-illumihating positions of the galvanometer in a circuit Yincluding the phototube, which steps comprise continuously acting in accordance with an independent variable to aect the position of the 'galvanometer relative to a normal position in 'which the light beam is only partially on the phototube, continuously -but sharply altering the 'e'iective time-constant of the circuit to produce Ca Irapid initial current response following a sud- 'd'e'n change in the position of the galvanometer within said range and a lower -nal rate of respense with a diie'rent order of "magnitude of equivalents. Where the expression physical lo the effective time-constant, and ZAlsubstantially Examiner oneness 9 continuously acting upon the galvanometer in accordance with the value of the damped current to bring the light beam to rest substantially at ats normal 3. '131e method of stably controlling a final element in correspondence with the value of an independent physical variable which is to be measused, whichcomprises altering the position of a member from a normal position in accordance .changes in the value of said variable, varying the value. of a physical condition of a governing system to ultimately correspond with the stated deflection of the member, sharply but continuously altering the time-constant of response of. the governing -system following any sudden change inthe position of the member near its normal vposition to abruptly reduce the rate of change in the condition after there is a substantial initial jump of the response, governing the position of a final element in accordance with the responsive value of said .physical condition but without correspondence of the last named position with the-last named value, and reacting upon the member in vaccordance with the position of the -final element to restore both the position of the member to a normal position and the value of the responsive condition to a normal value which ultimtely corresponds with said normal position and .in brimI the position of the nal element into correspondance with the value of the independent-variable.

4. in -an instrument of the measuring and con- :trolling class, in combination, va circuit, a member .which is deectable from its normal position in .response -to changes in the value of a variable which ris .to be .measured or controlled to vary an electrical current in said circuit in response to its deection, said Vcircuit including permanently conmected elements that continuously alter the ef- .iective time-constant ont the circuit to very sharp- .lymeduce the .rate of an initially rapid and appreciable response thereof directly following a sudden change in the deflection of the member, :and means governed by the thus-modified current :in the circuit for vreturning said member to its mormalposition.

i. In'an instrument of the measuring and conrolling class, the combination of a'member havding a xed natural period and positioned in rersnonse to the difference between an independent 'maniable `to be measured or controlled and a balflnclngyariable, a governing system including an -eltrical .circuit and a means in said circuit seny .nitive to said member to alter the value of an felectrlcal .condition in the circuit in response to @changes in the position of the member, said cir- .cuit Vbeing constructed to have a longer natural ipeod than that of the rst named means, an relectroresponsive means for rebalancing the amember, .and .relay means connected with the ielectroresponsive means and with the governing -cirmiit and constructed to operate at predeterlnnned current `values which include a dead-zone .of non-operation 'of the electroresponsive means :and to generatesel-contimng oscillations of the relay means V.of a shorter vperiod than that of the `member when .the lcurrent supplied to the relay rmeans is between xed limits which predetermine oscillating ranges surrounding said dead-zone, :whereby the action .of the relay means causes .intermittent operation of the balancing means .and hence operates said member toward a stable balancingfposition in steps.

6. hIn-.a measuring or controlling system-includcircuit having a -xed point and including a slidewire, .and a slide-wire contact movable by said motor for varying the E. M. F. of said movable contact relative to that of said xed point; a mirror galvanometer and a source of independently variable E. M. F. connected between said xed point Vand said movable contact in response to changes in said independently variable E. M. F. and the E. M. F. of said movable contact, said mirror galvanometer having a normal position corresponding to no current ow therethrough, a source vof light, and photoresponsive means so arranged that a light beam reflected by said mirrer is .directed towards said photoresponsive means, a .stop on .said galvanometer arranged relative to said mirror to prevent the deflection of its reected beam beyond said photoresponsive means on one side only; means for amplifying the current .from said photoresponsive means, and two relays connected by an amplifier circuit with said amplifyng means and operable at dilerent `values of the amplided current, said relays having contacts for controlling said motor and other contacts for altering the potential of said fixed point for affecting .the .relation between the movements of said galvanometer and said motor; the combination with said amplier circuit of means including a permanently connected capacitor and substantially constant cooperating resistors ineluded in said amplifying means to give a quick substantial change of current response of the amplifying means .following a sudden large increase of said illumination of the photoresponsive means to trap the -response at a predetermined vaine .intermediate to those corresponding to the operating values of .said relays and to maintain said predetermined value for an interval of time greater than the stopping times of said motor and said movable galvanometer; and additional contacts and associated capacitors and resistors for relays .which cause the latter to oscillate .when .said amplied current remains at a value 'intermediate to the vopening `and closing values of either relay and to predetermine the operating values of both relays, the oscillations being timed by .the relay characteristics and the values of said .resistors and capacitors connected to said last named contacts to have a shorter period than the .natural period of oscillation of the system.

V'7. 1n an instrument of the measuring and controlling class, in combination, a member displaceable from a normal zero position in accordance with the value of a physical condition to which it is responsive, an electrical circuit network including a means sensitive to the position of the member Yand in Awhich the current value in a portion of said network is modified in `response to a change in the position of the member to cause said current value to ultimately correspond with any stationary position of the member, relay means electrically connected to such portion of the circuit and constructed and arranged to operate at a predetermined value of said current, means operatively connected to said member and governed by said relay means to cause the movement of said member toward its normal zero positionfand a resistor for said relay means operatively connected thereby vto said circuit to maintain a substantially constant impedance value in said portion of the circuit so that the current therein is .not appreciably affected by the operation of said relay means.

8. A governing system fora controlled device comprising, in combination, a governing circuit .Qing c reversible motor, an electrical :measuring whichis connectable with a source ofcurrent supply, means connected with the circuit for modifying from a normal value the current in the circuit ln response to changes in the value of a physical variable, a means for controlling said device to restore said current to substantially its normal value at least operatively connected with the circuit and responsive to the current therein, and means permanently connected with the circuit for permitting an appreciable jump of, and

then damping the response of, the current upon a sudden one of the stated changes to cause said circuit to have a double time-constant of said response by very sharply reducing an initially high responsiveness by abruptly changing from an initial small time-constant to another having a different and very much larger order of magnitude, whereby a sudden change in the value of said variable is directly followed by a rapid and appreciable initial current response which tends to effect a prompt controlling operation of the controlling means, and the rate of the current response is suddenly reduced so that the initial rapid response is followed after such reduction by a much lower rate of response which gives the controlled device time to respond to an initial controlling action to strongly tend to restore the first named means to substantially its normal condition which, if steadily held, restores said current to substantially said normal value before the controlling means operates to further control the device.

9. In an instrument for measuring or controlling an independent physical variable and connectable to a source of said variable, the combination of a damped member having appreciable '35 inertia and continuously sensitive to the diierence between the independent variable and a balancing variable, a means for controlling the balancing variable, and a governing system operatively connecting the sensitive member with the `4,0

controlling means to govern the balancing, said governing system including a current-modifying means sensitive to the position of said member, a circuit network connected to the current-modifying means whereby the current in the network is altered in accordance with the position of said member, relay means connected in the network and to the controlling means and operative in accordance with the value of said current to cause the operation of said controlling means when the current is outside of a normal dead-zone ultimately corresponding with a substantially balanced position of the damped member, and means permanently connected in said circuit network to cause the network to have a double time-con- 5 immediate initiation of the rebalancing action of 'the means controlling the balancing variable and,

upon the members re-entry of the dead-zone, following a substantial departure therefrom, at a high enough velocity to otherwise overshoot the normal position of the far edge of the dead-zone,

Vto provide an immediate operation of the relay means to stop the controlling means for the balancing variable, and said permanently connected Cross Reference layed response which is greater than the damping of said damped member whereby, following such re-entry of the dead-zone, the stated relatively high damping at least in effect displaces the far edge of the dead-zone in the direction of motion of the member and farther than the travel of the member in that direction and to subsequently reduce the displacement of said far edge toward its normal position more slowly than the return of said member to within the normal dead-zone to then prevent a further operation of the relay means which would tend to keep the damped member from coming to rest.

10. In an instrument of the measuring and controlling class having a circuit attachable to a source of a variable electrical condition to be measured or controlled, a galvanometer connected with said circuit, together with a light source, a mirror, and a phototube, all arranged to position the reflected image of said light source relative to an edge of said phototube so that the phototube current corresponds with the galvanometer posi tion over an operating range in which at least part of the beam illuminates the phototube, and an electrically-responsive means for rebalancing the galvanometer, the combination of: an amplier circuit connected with the phototube and with the rebalancing means and constructed to amplify the phototube current in a portion of said amplier circuit which is connected with the rebalancing means to govern such means in accordance with the value of the amplified current and hence with the position of the galvanometer, and means permanently connected with said ampliiier circuit to cause it to have a double time-constant of response to provide an initial rapid, and a subsequent slow, rate of response of the ampliiied current in said amplifier circuit portion when said phototube edge is reached by said image in traveling onto or oli" from said phototube following a sudden change in the value of said variable electrical condition and hence in the position of said galvanometer.

11. In an instrument of the measuring and controlling class and including a motor control system having a circuit connectable to a source of a variable electrical condition to be measured or controlled, and also having a galvanometer connected with said circuit, together with a light source, a mirror and a phototube, all arranged .to position the reflected image of said light source .relative to an edge of said phototube so that the phototube current corresponds with the galvanometer position over an operating range in which at least part of the beam illuminates the phototube, and electrically-responsive relay means controlled by said phototube and means governed by said relay means for rebalancing the galvanometer, the combination of an amplier circuit connected with the phototube and with a Aportion of the relay means and constructed to amplify the phototube current to create a corresponding amplied current in said relay means portion to govern the stated rebalancing in accordance with the value of the amplified current and hence with the position of the galvanometer, and elements permanently connected with said ampliiier circuit providing a double time-constant of response for the amplified current to provide an initial rapid, and a subsequent slow, rate of response of the amplied current in said ampli- `ier circuit portion to a sudden change of illumination occurring when said phototube ledge is Examiner means also including elements to cause damping lreached by said image in traveling onto or oli' of Said current accompanying the second or de- ,5

from said phototube following a sudden change n n u moose 1l innthe value nf asxid'variable condition dead-none before `the nin-ent can be ichanged am! :hens-,erin the position of 'said galvanometen enough Sto eavse the 'dead-zone with :the result said iay f'meansbeing two in :number and intha't the :current attains Aand tends fto :stay benlmilngtwo relay coils carrying atleast a part of tween itssaidfllmiting'values. the yamplified current and having `contacts -op 5 M The'combination net forth .in claim 13 in erative 'at different values of `theramplitlerl -curwhichthememberiscontinuously sensitive to the rent, a series 'and a'slnmtresistor for each ofsaid stated 'difterence and the combination is provided reiayscoils, said contacts being arranged tonperawith an additional :means for modifying 'the baitively includeluith of said resistors in said -amanolng wariable independently of 4said electro pirtier circuit when the associated respective reresponsive means and `operatively. connected with lay means is closed and to operatively rexclude the relay means tobegoverned by .the'operation both when the associated respective means is ofthe latter.

Uilen. `115..An"-inxtrument'of the measuring and con- 12. In im instrument .-o'f Vthe measuring Jand trolling 'classcomprising in combination, a memmntrolling tclass, combination of va `men'iber 35 ber whose Vposiiaion S isensitive tothe difference whose position is responsive to a chmrge "in the metweenfthe values lof a physical -variable to .be @value of a physical condition to be measured or masuredror controlled and ora balancing physinonirolled; anielectrical .governing system includ- :cal Nariable; :an 'electrical :circuit Aand means jng n --circuit network, la means sensitive to 'the Ytherein which is 'operatively Connected With the position of :the :member and connected .wish the im member to .modify van electrical condition :of one circuit to modify the value of a current in a porportion 'of the circuit'and hence the value ofthe -tlon thereof from anormal value in accordance icurrentdzhereininrultimate correspondence with *with auch position, and 'means including a cafthe position of the member; .an electroresponsive pacitor connected :in another portion `of said cirmeans'for :controlling the value of the balancing Lcuit, :and nwo substantially constant resistors 225 variable; a imeans tor modifying the lbalancing which are l.permanently connected to said caxariable independently of said electroresponsive lpa-citar respectively in shunt and .in'seri theremeans; andztwo 'relay means connected with anwith; :andan .electroresponsive means connected other portion of Vthe circuit and operatively conwith still another portion of said circuit in lwhich mected withtheevariable controlling and .modify- 'lthe'cln'rent is modified by the last-named means il) ing means torgovern Atheir :respective operations, and operative in accordance with the value of a .each of said relay `means including a -coil concurrentinsuch portion torestore the value ofthe -nected 7with the circuit, contacts vand a resistor .modified current to said vnormal value; said caf-connected'by the contacts 'with .the coil to cause pacitor and resistors being of relative'magnitudes -a higher :opening than closing current value Vwhich produce an appreciable and .rapid initial 35 whereby oneof :the relay means oscillates its conanxrrent responseiin the last :named circuit portacts "when the value of thecurrent is between -tion with a very small time-constant directly the opem'ng and closing values of feither relay mfter =a sudden change in the position vof rthe means said relay 'means also having a .resistor fmember and with Aa sharp and great increase in connected therewith to cause one relay means the time-constant soon :afterwards to produce a 'l0 oscillating .range to be at a higher current value flow-gradual further iresponse 'of said current. than that of the xother lwhereby a dead-zone of 13. yan insti-mirent of the measuring Aand conoperation oflthe controlling and modifying means :trolling class, comprising, in combination, amem- 'issetnp .between'the'oscillating zones. lber 'whose position is sensitive to the difference T16. .Aninstrument of the measuring and con- -between .the values of a 'physical variable to 'be V.a5 -tmllng class comprising, in combination, a memzfmeasured or controlled andofabalanong Physi- T'ber whose position relative to anormal balancing .cai variable; 1an electrical :circuit 'and means Lposition.isisensitive totherdifference between the rtherein which is operatively connected .with lthe -values Tof a :physical variable Yto -be ,measured 'or qmember to 4modify nn electrical condition of one Iooutrolled and of a balancing variable; an elecportion 'of the circuit `andfhence .the value of fthe olo 'trial circuit and means therein which is operazcurrent therein in ultimate correspondence 'with -tively connected with the member to modify an the position of the member; anelectroresponsive :electrical condition of the circuit and hence the .means controlling the valneof the balancing varithe current therein in accordance with able; relay means connected-with another portion themosition of the member; an electroresponsive of the circuit and with the controlling means -to .555 -rebalancing means for controlling the value -of :govern the balancing operation.ofthelatter,said Lthe balancing variable; another rebalancing .relay means being constructed and arranged to means-operatively connected with said member fui limiting values of said current and -hence .-posito advance qit towards its normal balancing positions of the member which predetermine a dead- `tion to cause an earlier rebalancing than that -saone as regards the stated balancing operation; 50 ycaused by saidelectroresponsive means and op- .and means permanently connected in a ferative lindepexaaiently of said electroresponsive of the circuit intermediate vof the other -stated means; .twolrelay means connected with said cirportions and constructed and arranged relative cuit and operatively connected with both of said tosaid circuit to act independently of the operarebalancing means to govern their operation,each tion 'of the relay meansto'permit an appreciable of said relay means .being constructed to have a current response at a very low effective time-conhigher opening than closing current value wherestant of the circuitrdrectly after a sudden change by one portion of the relay means oscillates when of the position of the member and very soon the value of the current is between the opening afterwards to be very sharply increased, whereand closing values of either relay means, said by the response of said current, upon a re-entry 70 relay means also being constructed to have the of the members dead-zone by the member, is first oscillating range of one relay means at a higher large and rapid so that the operation of the relay current value than that of the other whereby a. means surely occurs and then slow so that both dead-zone of operation of both rebalancing the sensitive member and the controlling means means is set up between the oscillating zonesl have time to come to rest within the members 75 and each of said relay means includes means for o n a l preventing the operation of the relay means from directly appreclably affecting the current in the circuit; and means permanently connected in a portion of the circuit intermediate of the other stated portions and constructed and arranged relative to said circuit to act independently of the operation of the relay means to alter the timeconstant of the current response to upon a sudden change of the position of the member to be small directly after such change and very soon afterwards to be very sharply increased.

17. A governing system for a motor comprising, in combination, a governing circuit which is connectable with a source of current supply, photoresponsive means connected with the circuit for modifying the current therein in response to changes in its illumination, a motor-controlling means at least operatively connected with the circuit and responsive to the current therein, and means permanently connected with the circuit for permitting an appreciable jump of, and then damping, the response of the current to a sudden one of the stated changes to cause said circuit to have a double time-constant of said response by very sharply reducing an initially high responsiveness by abruptly changing from an initial small time-constant to another having a different and very much larger order of magnitude, whereby a sudden change in the value of said Variable is directly followed by a rapid and appreciable partial initial response which tends to effect a prompt controlling operation of the motor-controlling means, and the rate of current response is suddenly reduced so that the initial rapid response is followed after such reduction by a much lower rate of response which gives the motor time to respond to an initial controlling action before the controlling means operates to further control the motor.

18. In an instrument of the measuring and controlling class and including a circuit connectable with a source of a variable electrical condition to be measured or controlled, and also having a galvanometer connected with said circuit, together with a light source, a mirror, and a phototube, all arranged to position the reflected image of said light source relative to an edge of said phototube so that the phototube current corresponds with the galvanometer position over an operating range in which at least part of the beam illuminates the phototube, and an electroresponsive means for rebalancing the galvanometer, the combination of: an electronic amplifier including a plate, a grid, a lament and circuits connected thereto and to said phototube and to an alternating current supply, and two relay means connected in the plate and grid circuits in common and to the filament, said relay means being constructed to operate at different current values and including contacts which are connected to said electroresponsive means to balance said galvanometer in accordance with the operation of said relay means.

19. The combination set forth in claim 18, in

which one of said relay means includes a coil, a 55 resistor permanently shunting said coil, a resistor permanently connected in series with said shunted coil, a resistor connected only when said relay means is closed to shunt said coil and its series resistor, and means connected by said relay means when said relay means is opened to short said series resistor, whereby the relay means and hence the electro-responsive means is caused to intermittently operate to cause rebalancing by steps for slow changes of the value of the variable electrical condition.

20. In an instrument of the measuring and controlling class which includes a motor control system; a circuit connectable to a source of an electrical variable to be measured or controlled, and including a mirror galvanometer for directing a light beam relative to a photoresponsive means aiected thereby, an electronic amplifier of the current from said photoresponsive means, said amplifier including a control grid, and a circuit connecting said amplier with said photoresponsive means, means for rebalancing the galvanometer, and means connected with the last named circuit and including a motor for actuating the rebalancing means in accordance with the amplified current from the amplifier, the combination of a capacitor and a resistor permanently connected in series in only the control grid circuit of the amplifier circuit, and a high substantially constant resistance leak permanently shunting such series-connected capacitor and resistor, the values of said series capacitor-andresistor and of the shunting leak being such that a sudden change to a new level of the current from the photoresponsive means causes a sudden appreciable change in the control grid voltage and hence renders the motor control system highly responsive to sudden changes of the position of the galvanometer followed by a gradual change for stabilizing the instrument.

21. In an instrument of the measuring and controlling class having a relay-governed system, the combination of a circuit, a member which is deiiectable from a normal position upon a change of an independent variable to be measured or controlled and influencing the system, and said member being operatively connected to said circuit to alter the value of an electrical condition therein in response to the deflection of the member, said circuit including means permitting an initial substantial jump of the stated response and tor altering the effective time-constant of the circuit and continuously effective to sharply reduce an initially rapid rate of response of said condition when the response thereof approaches its nal -value, a nal movable element reacting upon said member, and means including relay -means operatively connected to said circuit and -to said element to move said element in accordance with the value of the electrical condition in the circuit to return the member toward its normal position following a deflection therefrom.

CHARLES O. FAIRCHILD. VOZCAN L. PARSEGIAN.

CERTIFICATE for CORRECTION. v 'Patent No 2 267'682. I. December 25, 1914.1.

CHARLES o. FAIRCRILD, RT AL.

It is hereby certified that error appears in the printed specificetion ofthe above numbered patent requiring Correction as follows: Page 2, second column, line 6h', after "following" insert =thnt; page b., first Colline )4.5, claim 1, strike out the word "noting"; psge 9, secondcolumn, line 29, claim 6, for"'substentia11yoonstant cooperating read "cooperating substantially constant--g line 68, claim?, for "to" first occurrence, read --in series withsaidrelaymens inf-f; pagev 12, first column, line 8, claim 16, before "upon" strike out "to"; and second column, line 27, claim 20, after "orf' inserts colon; and that the nid Letters patent should be read with this Correction therein-that the seme moy conform to the record of y the onse in the PatentvOifice.

Signed and. sealed this'lOth dey of February, A. D. 1914.2.A

Henry Vm4 Arsdale, (Seel) Acting Commissioner of Patents. 

